1. Field of the Invention
The present invention relates to improved endotracheal tubes and devices for use in conjunction with such tubes. More particularly, the present invention is directed to endotracheal tubes which employ a carbon dioxide indicator to determine proper placement of the tubes in the trachea.
2. Description of the Relevant Art
Accidental undetected esophageal intubation remains a major cause of anesthetic death and disability. In the anesthetized, paralyzed patient, as well as in the victim of injury or illness, an endotracheal tube is placed to secure the airway, permit controlled ventilation, and prevent the risk of vomiting with the aspiration of gastric contents. Ventilation of the lungs is essential to life. It is the mechanism by which oxygen is carried into the body and carbon dioxide, a constant product of metabolism, is eliminated. The apneic patient, whether as a result of anesthesia, cardiac arrest, injury, respiratory failure or airway obstruction must be artificially ventilated in order to survive. Unfortunately during the attempted endotracheal intubation, the esophagus is sometimes accidentally intubated. If this error is detected quickly, no damage results. However, if this condition is permitted to persist for even a few minutes, brain injury and death occur.
The laryngoscopist attempts to pass the endotracheal tube into the tachea under direct vision. Unfortunately, this is not always possible. Routine measures to confirm proper tube placement include visual inspection of the chest, ausculation of the chest and upper abdomen, observation of the endotracheal tube for condensation during expiration, use of EKG, precordial and esophageal stethoscopes, and frequent monitoring of vital signs. In spite of these measures, undetected esophageal intubations continue to occur with the predictable disastrous results.
Confirmation of proper tube placement can be based upon the fact that carbon dioxide, a product of metabolism, is always present in exhaled air in approximately 5% concentration, but is present in esophageal gas in only minute concentrations. The capnograph and mass spectrometer are two instruments which have gained limited use in the operating room to detect proper endotracheal tube placement. Both depend upon the presence of carbon dioxide to make the determination. However, both are expensive instruments, beyond the budget of many hospitals and unavailable at the scene of an accident or cardiac arrest, in the ambulance, or the emergency room. Additionally, both are subject to calibration errors and in the case of the mass spectrometer, there may be an intolerably long delay before the carbon dioxide tension is determined.
A third device, the "Einstein CO.sub.2 Detector" was described in. Berman et al. (1984). Anesthesiology, 60: 613-614. The Einstein Detector utilizes a deLee mucus trap containing an aqueous colorimetric carbon dioxide indicator in line with an endotracheal tube. Unfortunately, the Einstein CO.sub.2 Detector has failed to gain even limited acceptance for it is messy, time consuming, and requires that the detector be disconnected from the breathing circuit before air can pass bidirectionally through the endotracheal tube. Clearly, then, the ideal CO.sub.2 detector has not yet arrived on the health care scene.
This ideal detector should be inexpensive, reliable, and simple. It should not require, nor be subject to errors of calibration. It should be capable of being incorporated into the endotracheal tube or breathing circuit so that disconnection is unnecessary and so that it will not add to the burgeoning assortment of equipment and instrumentation already threatening to choke the operating room and topple the anesthesia machine. At the scene of accidents or heart attacks, where conditions are difficult and the laryngoscopist likely to be less experienced, the need for a reliable, self-contained CO.sub.2 detector is great.